The present invention relates to a sensor for glide height testing, and more particularly to a test slider assembly including a piezoelectric sensor for detecting asperities on the surface of a disc.
In order to certify that a magnetic disc is adequately smooth for use in a disc drive system, glide height tests must be performed on the disc. Glide height testing is used to verify that a magnetic recording disc is able to accommodate a specified glide height. As the density of data recorded on magnetic discs continues to increase, the flying height of magnetic transducers with respect to the disc must be reduced to accurately read and write information on the disc. As a result, the magnetic recording disc must accommodate the lower glide height of the transducer and the slider supporting it, meaning that the disc surface must be extremely smooth and uniform.
In addition to the general requirement of reduced glide height, magnetoresistive (MR) heads, which utilize an active head element made of a thin layer of NiFe, are extremely sensitive to small physical defects in the surface of the disc, such as undulations on the disc surface and microscopic debris on the disc. When the MR head strikes a defect, there is a momentary frictional heating of the MR element, known as a thermal asperity. This heating effect increases the resistance of the MR head, which causes data errors and loss of information in reading the disc.
A common type of glide height testing is performed by utilizing a test slider having a piezoelectric element bonded thereon. When any part of the slider contacts a protrusion on the surface of the disc, the slider vibrates from the impact. The piezoelectric element bonded to the slider senses the vibration forces acting on the slider, and exhibits a voltage between its terminals representative of the forces experienced by the element. If the vibration force sensed by the piezoelectric element exceeds a predetermined design level, or if vibration occurrences exceed a predetermined design frequency, the disc media under test is not adequately smooth to be used in applications at the glide height being tested.
Previous glide height test sliders mounted the piezoelectric sensor on the slider with a portion of the piezoelectric element extending over the slider edges so that the piezoelectric element could be wired from the top and bottom sides, enabling detection of the voltage across the piezoelectric element by wires connected to each side of the element. However, the extension of the piezoelectric element and the wires connected to the sides of the element created one or more "wings" in the slider or in the piezoelectric element itself, thereby affecting the flying characteristics of the slider and inducing additional vibrational modes. The response of the slider to asperities on the disc media was altered, making it more difficult to accurately deduce the asperity characteristics of the disc from vibrations of the slider. Therefore, there is a need for a glide height test sensor which operates with a test slider without disturbing the original vibrational modes of the slider.